It sounds as if you have enabled the 'Open Graph - K2' plugin on your site. Go into JFBConnect > Open Graph > Objects. If there is an object set up for your K2 Items, then please edit it and make sure the 'Description Type' field is set to Meta. Since you have been setting the meta description in each K2 item, that description will be set in the metatags and thus by JFBConnect. If you do not have any Objects set up, please create a new one and make sure you use Meta, since the 'Intro Words' is the default value.
I hope this explains the issue, but please let me know if you have further problems.
Thanks
-Melissa